Process of preparing aluminum chlorhydroxides and aluminum hydroxide



Dec. 10, 1963 JONES 3 113,911

J. L. PROCESS OF PREPARING ALUMINUM CHLORHYDROXIDES AND ALUMINUMHYDROXIDE Filed Sept. 6, 1960 3,ll3,9ll

Patented Dec. 10, 1963 3,113,911 PROCES F PREPARING ALUMINUM CHMHYDROXEBES AND ALUMINUM HYDRGXIDE John Jones, Berkeley Heights, NJ.,assignor, by mesne ass gnments, to Armour Pharmaceutical Company,Chicago, Ill a corporation of Delaware Filed Sept. 6, 1969, Ser. No.54,144 9 Claims. (61. zet -94) Th s invention relates to a process ofpreparing aluminum chlorhydroxides, particularly Al (OI-I) Cl, the -76basic salt, by electrolysis of aluminum chloride, and to an apparatusfor carrying out this process.

The electrolysis of aluminum chloride to produce aluminum chlorhydroxideAl (OH) Cl is described in US. Patent No. 2,392,531. An aqueous solutionof aluminum chloride is subjected to electrolysis in a diaphragm cell inwhich catholyte and anolyte are kept in separate compartments. III thecourse of this process, hydrogen is liberated at the cathode andchlorine at the anode. The reaction is quantitative, so far as theelectrolysis of aluminum chloride is concerned. The yield of aluminumchlorhydroxide is not good, however, because of the loss of chlorine atthe anode. In order to make the process practical commercially, it isnecessary to recover this chlorine, but this is rather difficult to do,and there is also the problem of its contamination with other materials.Consequently, the electrolytic production of aluminum chlorhydroxide hasnever been fully satisfactory.

In accordance with the instant invention, a process of preparingaluminum chlorhydroxides and aluminum hydroxide by electrolysis ofaluminum chloride as the catholyte is provided wherein the loss ofchlorine at the anode is prevented by reaction of such chloride ion asmigrates from the cathode compartment with aluminum oxide before itreaches the anode compartment, regenerating aluminum chloride, which canbe recirculated to the cathode compartment for conversion to aluminumchlorhydroxide. The reactions which take place in this electrolysis canbe summarized as follows, using the /6 basic salt as illustrative.

In cathode compartment:

H. 2AlC1 +5 OH- A1 OH C1+5 Cl 40 In compartment adjacent cathodecompartment:

III. 2A1 O 6HCl- 2AlCl 3H O In anode compartment: 59

IV. 2H O- O +4H+ It will be apparent that similar reactions occur in theformation of other aluminum chlorhydroxides and aluminum hydroxide. Theprocess can be made to produce any of the compounds, including, forexample:

Mixtures of these also can be obtained. The electrolysis proceeds downthe series from No. 1 to No. 6, as the ultimate product, and can befollowed by observing the pH of the reaction mixture, which ranges fromabout 1 at the start to about 4.4 at No. 5, the other aluminumchlorhydroxides being intermediate, and the aluminum hydroxide is formedas a precipitate at the end stage of the electrolysis. Hence, anydesired aluminum chlorhydroxide can be prepared simply by stopping theelectrolysis at the pH value corresponding to the desiredchlorhydroxide.

The anolyte plays no role in these reactions, and preferably is keptisolated therefrom so that chloride ion cannot migrate into it.

It is apparent from the above scheme that one mole of hydrogen chlorideis consumed for every mole of Al (OH) Cl produced. Hence, to start thereaction initially it is necessary to have hydrogen chloride present inthe aluminum oxide compartment, at least in the proportion of one moleof hydrogen chloride for every mole of aluminum chlorhydroxide Al (OH)C1 produced. If other aluminum chlorhydroxides are desired, such as the/3 basic salt Al (OH) Cl,, or the /3 basic salt Al (OH) Cl the amount ofhydrogen chloride will be increased accordingly. The overall effect ofthe process, therefore, as shown, is to convert water, aluminum oxideand hydrogen chloride into aluminum chlorhydroxide, hydrogen and oxygen.

The process of the invention can be carried out continuously orsemicontinuously or batchwise in an electrolytic cell having threecompartments, a cathode compartment, an anode compartment, and a thirdcompartment intermediate these two compartments. The type of cellcontemplated is shown in cross-section in the FIGURE.

The cathode compartment 1 is equipped with a cathode 2 of material whichis not attacked by aqueous aluminum chloride solution, such as carbon.The anode compartment 3 is equipped with an anode 4- of acidresistantmaterial such as platinum. The anode and cathode compartments areseparated from the intermediate compartment 5 by diaphragms 6 and 7,which permit the passage of ions required for carrying out the reactionsof the invention in their respective compartments, and preferablyprevent passage of all others.

In operation, the catholyte, aqueous aluminum chloride solution, isplaced in the cathode compartment, and the anolyte, an aqueous acidwhose anion is not discharged as a gas at the anode, such as sulfuricacid, is put in the anode compartment. An aqueous slurry of aluminumoxide containing as much hydrogen chloride as is required to start thereaction is put in the intermediate compartment 5. Then the electrolysisis begun.

In the cathode compartment, hydrogen gas: is discharged at the cathode,leaving behind Ol-I ion, and resulting in the formation of 1Xl((')I-I),,Cl in the catholyte, Where n represents the proportion of OHion in the product, and can range from 1 to 6. When n is 6, the productis aluminum hydroxide. Chloride ion from the cathode compartment andhydrogen ion from the anode compartment migrate into the intermediatecompartment, and there react with aluminum oxide in accordance withreaction HI above to form aluminum chloride. The conditions are soadjusted that a minimum of chloride ion migrates from the intermediatecompartment into the anode compartment, inasmuch as chloride ion in theanolyte could be discharged at the anode to form chlorine gas, reducingthe yield.

While diaphragms of any of the types commonly employed in diaphragmcells can be used between the various compartments in this cell, it ispreferred that the diaphragm between the anode compartment and theintermediate compartment be of cation-permselective material which willnot pass chlorine ion. This excludes chlorine ion entirely from theanode compartment. A variety of cation-permselective membrane materialuseful as diaphragms in electrolytic cells are known to those in theart. Such permselective membranes are in general to those of two types.One type is in the form of sheets, or films formed wholly of thecation-permselective material, such as are described, for example, inUS. Patents Nos. 2,636,851 to Juda et al., 2,702,272 to Kasper,2,730,768, 2,731,408, 2,731,411, 2,756,202 to Clarke, 2,805,196 toRoebersen et al., and 2,858,264 and 2,867,575 to De long. Thesemembranes can be formed directly from monomeric or unpolymerizedreactive ingredients, polymerizing them under conditions such that thedesired film is formed. The reactive ingredients may include thefunctional cationexchange groups, or such groups may be incorporated inthe film after its formation by appropriate reaction procedures, all ofwhich are well known in the art. Suitable acidic functional groupslinked to the matrix include SO3H and CO'OH groups, the former beingpreferred because of its high dissociation constant. Typical polymericmatrices to which such functional groups are linked include polystyrene,phenol-aldehyde resins, polystyrene-divinyl benzene copolymers,resorcinol-aldehyde polymers, copolymers of divinyl benzene with acrylicacid, copolymers of divinyl benzene with maleic anhydride, copolymers ofdivinyl benzene with acrylonitrile, copolymers of divinyl benzene andmethacrylic acid, cellulose derivatives such as regenerated cellulose,ethyl cellulose and polyvinyl alcohol, and like polymers containing freehydroxyl groups, reactedwith sulfonating agents, and polyethylenereacted with chlorosulfonic acids or other sulfonating agents. Examplesof such membranes will be found in the patents referred to.

The cation-exchange resins which can be employed in either of thesetypes of films include the sulfonated phenol aldehyde resins describedin U.S. Patents Nos. 2,184,943, 2,195,196, 2,204,539, 2,228,159,2,228,160, 2,230,641, 2,259,455, 2,285,750, 2,319,959 and 2,361,754, thesulfonated cross-linked polymers of styrene described in US. Patent No.2,366,007, and the carboxylic resins described in Patents Nos. 2,340,110and 2,340,111.

Porous diaphragms of other materials can be used, such as porous bondedmats or bats of nonwoven chemically resistant fibers, such as glass,asbestos, alundum, nylon and polyacrylonitrile fibers. Perforated platesand microporous corrosion-resistant metal and synthetic resin membranesalso can be employed.

The reaction temperatures are not critical. The formation of aluminumchlorhydroxide in the cathode compartment is favored by electrolysis ata temperature above about 70 C. At lower temperatures, there is atendency to form aluminum hydroxide, which may precipitate out. Theupper temperature limit is determined by the boiling point of thecatholyte, and is usually approximately The reaction of aluminum oxidewith chloride ion or hydrogen chloride to form aluminum chloride in theintermediate compartment proceeds at elevated temperatures, above about70 C. Thus the reaction proceeds with good efiiciency at thetemperatures applied in the cathode com- .paItment.

Chloride ion migration from the intermediate compartment into the anodecompartment is less at low temperatures, and it is accordingly preferredthat the anode compartment be kept at room temperature or below, or atleast as close to room temperature as is convenient. Ionpermselectivemembranes tend to lose their efiiciency in barring passage of ions astemperature increases, and this is an additional reason for maintainingthe anolyte at as low a temperature as possible.

The desired temperature gradient from the cathode compartment to theanode compartment can be achieved by interposing cooling coils in theintermediate compartment adjacent the diaphragm separating theintermediate and anode compartments. The diaphragm would be on the anodeside of the cooling coils. Other ways of achieving temperature gradientsare known to the art, and are disclosed in the literature on diaphragmtype cells, inasmuch as this problem is encountered in other processes.

The concentration of aluminum chloride in the catholyte can be modifiedas desired, according to the particular aluminum chlorhydroxide that isdesired. Solutions of aluminum chloride ranging from about 5 to about25% AlCl are satisfactory. Usually, the maximum concentration that canbe obtained without too high a viscosity is used, because this avoidsthe necessity of concentrating the anolyte solution, since the aluminumchlorhydroxide is ordinarily sold as a 50% aqueous solu tion.

The concentration of aluminum oxide in the slurry in the intermediatecompartment will be determined by the aluminum chloride concentrationand the amount of migration of chloride ion from the catholyte into thatcompartment. More aluminum oxide may be required per mole of aluminumchloride when the /6 basic salt is produced, for example, because morechloride ion is available to migrate into the intermediate compartment.However, it is also possible in a semicontinuous or continuous processto adjust for different concentrations of aluminum chloride and aluminumoxide simply by modifying the rate of removal of the liquor from thesecompartments to correspond to the amounts of aluminum chlorhydroxide andaluminum chloride, respectively, that are formed therein.

The amount of acid required in the anode compartment is simply enough topermit eflicient electrolysis. An 0.5 to 10% solution of a strong acid,such as sulfuric acid, is quite satisfactory. A somewhat greaterconcentration of a Weaker acid, such as phosphoric acid, may benecessary because of the lesser ionization of the acid to achieve thesame current efliciency as is obtained at these sulfuric acidconcentrations.

The following examples in the opinion of the inventor represent the bestembodiments of this invention:

Example 1 A diaphragm cell was employed in this run, of the type shownin FIGURE 1. The diaphragms separating the cathode and anodecompartments from the intermediate compartment were made of porousalundum sheet. 195 g. (0.3 mole) of a 24 Baum solution of aluminumchloride was placed in the cathode compartment, which was equipped witha carbon cathode. A slurry of 30 g. of aluminum oxide and 5 ml. ofhydrogen chloride (2.17 g. chlorine) in 500 ml. of water was put in theintermediate compartment, and ml. of 10% aqueous sulfuric acid solutionwas put in the anode compartment, which was equipped with a platinumanode. The aluminum oxide slurry was prepared by mixing the water andhydrogen chloride, and bringing the resulting solution to a boil, afterwhich the aluminum oxide was added.

The catholyte was brought to a temperature of 94 to 98 C., and thecurrent then turned on. A current of 2 amperes was applied for 4.5hours. 8.5 volts was required at first. After one hour, this had droppedto 6 volts. The current was then changed to 1 ampere for 0.5 hour, atthe end of which time the pH of the catholyte was 3.25. The current wascontinued at 1 ampere for three hours, after which the voltage haddropped to 4, and the pH was 4.2.

135.6 g. of catholyte were obtained, having an aluminum content of2.79%, and a chlorine content of 1.85%. Thus the aluminumzchloride ratioAl/Cl was 1.98. The ratio for A1 (OH) Cl is 2, showing that the productwas quite pure.

The liquor in the intermediate compartment showed that 15.2 g. ofaluminum oxide was dissolved. The aluminum content was 1.27% and thechlorine content 4.14%. Thus, the Al/Cl ratio was 0.39. This ratio forAlCl is 0.33, showing a very significant conversion of aluminum oxide toaluminum chloride.

The anolyte liquor weighed 131 g., and contained 0.05% aluminum and0.116% chlorine.

Example 2 The electrolytic cell employed in this run was the same asused in Example 1. 390 g. (0.6 mole) of a 24 Baum solution of aluminumchloride was placed in the cathode compartment. A slurry, prepared asset forth in Example 1, of 40 g. of aluminum oxide and 5 ml. ofconcentrated hydrochloric acid (2.17 g. chlorine) in 500 ml. of waterwas placed in the intermediate compartment. 150 m1. of a aqueoussulfuric acid solution was placed in the anode compartment.

The electrolysis was conducted for a total of 22.75 ampere hours at atemperature of 95 to 96 C. in the cathode compartment. The first sevenhours were at a current of 3 amperes. At the end of this time, the pHwas 3.3, and the voltage 6.2. The current was reduced to 1.5 amperes at0.75 hour at 6 volts and to 1 ampere for 0.25 hour at 5 volts. The pHthen was 3.75. The current was stopped after an additional 0.42 hour at1 ampere and 6 volts. The pH then was 4.35.

150.5 g. of catholyte were recovered, containing 4% aluminum and 2.62%chlorine. This corresponded to an Al/Cl ratio of 2.005, substantiallypure Al (OH) C1.

Analysis of the slurry in the intermediate compartment showed that 21.2g. of aluminum oxide had reacted. The aluminum content was 2.79%, andthe chlorine content 9.34%, giving an Al/Cl ratio of corresponding veryclosely to the theoretical ratio of AlCl which is 0.33. The SO contentwas 2.12%.

115.7 g. of anolyte was recovered, containing 0.37% aluminum and 1.14%chlorine.

Example 3 The diaphragm cell similar to that described in FIG- URE 1 wasemployed to prepare an aluminum chlorhydroxide having an Al/Cl ratio of2.06, essentially pure Al (OH) Cl. The diaphragm separating the cathodeand intermediate compartment was made of inch medium porosity alundumsheet. The diaphragm separating the anode and intermediate compartmentswas a sheet of cation exchange membrane of the sulfonated polystyrenetype, comprising particles of sulfonated polystyrene bonded togetherwith an inert resinous binder. The resin is available commercially underthe trade name Permutit Q, and the membrane is sold under the tradedesignation Permutit 3142. In place of this membrane, equally goodresults are obtained employing the strongly acid sulfonated copolymer ofstyrene and divinyl benzene prepared in sheet form in accordance withExample 4 of Patent No. 2,636,851.

In the cathode compartment containing a graphite electrode was placed780 g. (1.20 moles) of 24 Baum aluminum chloride solution. Theintermediate compartment was filled with a slurry of 200 g. of hydratedalumina (130 g. A1 0 50 ml. of concentrated hydrochloric acid (21.7 g.chlorine, and about 9 liters of water). Into the anode compartmentcontaining a platinum electrode was placed 9.3 liters of 0.95% sulfuricacid solution. The catholyte was brought to a temperature of 95 C. andthe current then turned on. The temperature was maintained at from 95 to105 C. in the cathode compartment, 79 to 81 C. in the intermediatecompartment and 30 to 33 C. in the anode compartment. A current 3amperes was applied over a period of 31.5 hours, at which point acoating of aluminum oxide was detected on the cathode, and the pH of thecatholyte was 4.2.

The catholyte was filtered, and yielded 388 g. of aluminum and 4.20%chlorine, the atomic Al/Cl ratio being 2.06. The intermediatecompartment yielded 10,030, g. of liquor, assaying 0.152% aluminum and1.19% chlorine, showing that 72 g. of aluminum chloride was formedduring the reaction.

Example 4 The electrolytic cell in this example shown in FIGURE 1 wasemployed to prepare an aluminum chlorhydroxide of approximately thecomposition Al (OH) Cl i.e., a mixture of some Al (OH) Cl with, mostly,Al (OI-I) Cl The cathode compartment contained 780 g. (1.20 moles) of a24 Baum aluminum chloride solution. The intermediate compartmentcontained a slurry of 200 g. of hydrated alumina (130 g. A1 0 100 ml. ofconcentrated hydrochloric acid (43.4 g. of chlorine) and 9 liters ofwater. The anode compartment contained 9 liters of 0.59% sulfuric acidsolution. The catholyte was brought to a temperature of C. and held at95 to C. for the duration of the run. During this period, theintermediate compartment temperature was held within the range from 82to 85 C., and the anode compartment at within the range from 33 to 36 C.

A current of 3 amperes was applied as soon as the catholyte had beenbrought to 95 C., and the current was continued for 19.5 hours, at theend of which time the pH of the catholyte had risen to 3.3. Thecatholyte was clarified by filtration, and yielded 331 g. of productassaying 7.09% aluminum and 6.42% chlorine, for an atomic Al/Cl ratio of1.45.

The intermediate compartment yielded 12,000 g. of liquor assaying 0.104%aluminum and 1.01% chlorine, showing that 39.4 g. of aluminum chloridewas produced.

Example 5 The electrolytic cell used in Example 1 was employed toprepare an aluminum chlorhydroxide having the approximate composition Al(OH) Cl Into the cathode compartment was placed 780 g. (1.2 mole) of a24 Baum aluminum chloride solution. The intermediate compartment wasfilled with a slurry of 200 g. of hydrated alumina g. A1 03), ml. ofconcentrated hydrochloric acid (65.1 g. of chlorine) and 9 liters ofwater. The anode compartment contained 9 liters of 0.59% sulfuric acidsolution. The catholyte was brought to 95 C. and held at from 95 to 100C. throughout the electrolysis. The intermediate compartment was held at83 to 85 C., and the anolyte at 33 to 35 C. during the run.

The current was turned on as soon as the catholyte had reached 95 C.,and was applied over a period of 15.25 hours, at which point the pH ofthe catholyte had reached 2.7. The catholyte was clarified byfiltration, and 438 g. of product recovered, assaying 6.00% aluminum and10.9% chlorine, indicating an Al/Cl ratio of 0.72. 30.6 g. of aluminumchloride was produced in the intermediate compartment.

I claim:

1. In the process for preparing aluminum chlorhydroxides and aluminumhydroxide from aluminum chloride by electrolyzing an aqueous solution ofaluminum chloride as catholyte to liberate hydrogen at the cathode, andform aluminum chlorhydroxides in the catholyte, the improvement whichcomprises contacting chloride ions migrating towards the anode withaluminum oxide to form aluminum chloride.

2. A process for preparing aluminum chlorhydroxides and aluminumhydroxide from aluminum chloride, which comprises electrolyzing in acompartmented cell an aqueous solution of aluminum chloride ascatholyte, thereby liberating hydrogen and forming aluminumchlorhydroxides and aluminum hydroxide in the catholyte, contactingchloride ions migrating towards the anode, with aluminum oxide to formaluminum chloride.

3. A process in accordance with claim 2 in which the proportions ofaluminum chloride and the conditions during electrolysis are so adjustedas to produce principally aluminum monochlorhydroxide Al (OH) C1.

4. A process in accordance with claim 2 in which the proportions ofaluminum chloride and the conditions during electrolysis are so adjustedas to produce principally aluminum dichlorhydroxide Al (OH) C1 5. Aprocess in accordance with claim 2 in which the proportions of aluminumchloride and the conditions dur- 7 ing electrolysis are so adjusted asto produce principally aluminum tetrachlorhydroxide Al (OH) Cl 6. Aprocess in accordance with claim 2 in which the catholyte is held at atemperature within the range from at least 70 C. up to the boiling pointof the catholyte.

7. A process in accordance with claim 2 in which the anolyte is anaqueous solution of an inorganic acid whose anion is not discharged as agas at the anode.

8. A process in accordance with claim 7 in which the acid is sulfuricacid.

9. A process for continuously producing aluminum chlorhydroxides andaluminum hydroxide from aluminum chloride in a compartmented cell havingcathode, anode and intermediate compartments, which compriseselectrolyzing an aqeuous solution of aluminum chloride as catholyte,thereby liberating hydrogen and forming aluminum chlorhydroxide andaluminum hydroxide in the catholyte, reacting chloride ion whichmigrates into an intermediate compartment of the cell with aluminumoxide to form aluminum chloride, continuously withdrawing catholyte andrecovering aluminum chlorhydroxides there from, continuously supplyingaluminum oxide and hydrogen chloride to the intermediate compartment,and continuously withdrawing aluminum chloride from the intermediatecompartment and recirculating this to the cathode compartment.

References Cited in the file of this patent UNITED STATES PATENTS2,176,343 Howard Oct. 17, 1939 2,392,531 Huehn et a1 Jan. 8, 19462,921,005 Bodamer Jan. 12, 1960 2,967,806 Osborne et a1 Jan. 10. 19613,017,338 Butler et al Jan. 16, 1962 OTHER REFERENCES Ephraim: InorganicChemistry, 5th edition, page 283.

1. IN THE PROCESS FOR PREPARING ALUMINUM CHLORHYDROXIDES AND ALUMINUMHYDROXIDE FROM ALUMINUM CHLORIDE BY ELECTROLYZING AN AQUEOUS SOLUTION OFALUMINUM CHLORIDE AS CATHOLYTE TO LIBERATE HYDROGEN AT THE CATHODE, ANDFORM ALUMINUM CHLORHYDROXIDES IN THE CATHOLYTE, THE IMPROVEMENT WHICHCOMPRISES CONTACTING CHLORIDE IONS MIGRATING TOWARDS THE ANODE WITHALUMINUM OXIDE TO FORM ALUMINUM CHLORIDE.